Charged Particle Beam Device and Analysis Method

ABSTRACT

A charged particle beam device includes: a charged particle beam source; an analyzer that analyzes and detects particles including secondary electrons and backscattered charged particles that are emitted from a specimen by irradiating the specimen with a primary charged particle beam emitted from the charged particle beam source; a bias voltage applying unit that applies a bias voltage to the specimen; and an analysis unit that extracts a signal component of the secondary electrons based on a first spectrum obtained by detecting the particles with the analyzer in a state where a first bias voltage is applied to the specimen, and a second spectrum obtained by detecting the particles with the analyzer in a state where a second bias voltage different from the first bias voltage is applied to the specimen.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2019-166868 filed Sep. 13, 2019, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a charged particle beam device and ananalysis method.

Description of Related Art

Electrons emitted from the surface of a solid specimen upon irradiationof an electron beam thereto are roughly divided into secondary electronsand backscattered electrons. The secondary electrons are electrons thatintrinsically exist in the specimen and have important information aboutthe surface state of the specimen such as the surface form, workfunction, and Auger electrons. Meanwhile, the backscattered electronsare electrons that are injected by an incident electron beam and haveinformation about a crystal structure in a slightly deeper level thanthe surface of the specimen, such as an average atomic number, crystalorientation, and plasmon loss of the specimen.

Here, electrostatic energy U_(T) of electrons can be expressed as thesum of the kinetic energy K of the electrons and potential energy P at alocation, where the electrons are generated, as in expression below.

U _(T) =K+P (eV)

The electrostatic energy U_(T) is always constant according to theenergy conservation law.

In a typical electron microscope, the kinetic energy K of electronsgenerated by an electron gun is nearly zero, and the potential energy Pof electrons generated by the electron gun becomes E_(P) underacceleration voltage E_(P). For the electrons generated by the electrongun, K=0 and P=E_(P). The specimen is irradiated with the electronsgenerated by the electron gun, with the electrostatic energy thereofbeing maintained, and the potential energy P of the electrons becomeszero on a grounded specimen surface, whereby the kinetic energy K of theelectrons is E_(P). More specifically, K=E_(P) and P=0 hold for theelectrons at the grounded specimen surface.

Since the potential energy P of the secondary electrons generated at thespecimen surface is always zero (P=0) as long as the surface isgrounded, the energy of the secondary electrons generated at thespecimen surface is entirely equal to kinetic energy K. The Augerelectron spectroscopy uses this relation and spectroscopically analyzesthe kinetic energy of the generated secondary electrons, therebydetecting Auger peaks to perform elemental analysis.

However, according to the method, the secondary electrons andbackscattered electrons cannot be distinguished from each other.Therefore, a total electron spectrum, obtained by combining thesecondary electrons and the backscattered electrons, has to be measured,and this increases the background and lowers the sensitivity.

For example, JP-A-7-192679 discloses an electron microscope, in which anelectromagnetic field that separates the orbits of backscatteredelectrons and secondary electros generated at a specimen is provided onan optical system from an electron source to the specimen and in which abackscattered electron detector that detects backscattered electrons isprovided on the orbit of the generated backscattered electrons, wherebythe secondary electrons and the backscattered electrons, which aregenerated from the specimen, are separated and therefore a backscatteredelectron signal can efficiently be detected.

In the analysis method such as Auger electron spectroscopy describedabove, when a signal derived from secondary electrons and a signalderived from backscattered electrons can be distinguished, higherquality analysis can be performed.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided acharged particle beam device including:

a charged particle beam source;

an analyzer that analyzes and detects particles including secondaryelectrons and backscattered charged particles that are emitted from aspecimen by irradiating the specimen with a primary charged particlebeam emitted from the charged particle beam source;

a bias voltage applying unit that applies a bias voltage to thespecimen; and

an analysis unit that extracts a signal component of the secondaryelectrons based on a first spectrum obtained by detecting the particleswith the analyzer in a state where a first bias voltage is applied tothe specimen, and a second spectrum obtained by detecting the particleswith the analyzer in a state where a second bias voltage different fromthe first bias voltage is applied to the specimen.

According to a second aspect of the invention, there is provided acharged particle beam device including:

a charged particle beam source;

an energy applying unit that varies kinetic energy of a primary chargedparticle beam emitted from the charged particle beam source;

an analyzer that analyzes and detects particles including secondaryelectrons and backscattered charged particles that are emitted from aspecimen by irradiating the specimen with the primary charged particlebeam; and

an analysis unit that extracts a signal component of the backscatteredcharged particles based on a first spectrum obtained by detecting theparticles with the analyzer in a state where the kinetic energy of theprimary charged particle beam has been varied into first kinetic energy,and a second spectrum obtained by detecting the particles with theanalyzer in a state where the kinetic energy of the primary chargedparticle beam has been varied into second kinetic energy different fromthe first kinetic energy.

According to a third aspect of the invention, there is provided ananalysis method for use in a charged particle beam device including acharged particle beam source and an analyzer that analyzes and detectsparticles including secondary electrons and backscattered chargedparticles that are emitted from a specimen by irradiating the specimenwith a primary charged particle beam emitted from the charged particlebeam source, the analysis method including:

obtaining a first spectrum obtained by detecting the particles with theanalyzer in a state where a first bias voltage is applied to thespecimen;

obtaining a second spectrum obtained by detecting the particles with theanalyzer in a state where a second bias voltage different from the firstbias voltage is applied to the specimen; and

extracting a signal component of the secondary electrons based on thefirst spectrum and the second spectrum.

According to a fourth aspect of the invention, there is provided ananalysis method for use in a charged particle beam device including acharged particle beam source and an analyzer that analyzes and detectsparticles including secondary electrons and backscattered chargedparticles that are emitted from a specimen by irradiating the specimenwith a primary charged particle beam emitted from the charged particlebeam source, the analysis method including:

obtaining a first spectrum obtained by detecting the particles with theanalyzer in a state where kinetic energy of the primary charged particlebeam has been varied into first kinetic energy;

obtaining a second spectrum obtained by detecting the particles with theanalyzer in a state where the kinetic energy of the primary chargedparticle beam has been varied into second kinetic energy different fromthe first kinetic energy; and extracting a signal component of thebackscattered charged particles based on the first spectrum and thesecond spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an electronmicroscope according to a first embodiment of the invention.

FIG. 2 is a graph illustrating an energy distribution of electronsemitted from a specimen surface.

FIG. 3 is a graph illustrating an energy distribution of electronsemitted from a specimen surface when bias voltage is varied.

FIG. 4 is a graph illustrating change in spectrum when a bias voltage isvaried.

FIG. 5 is a graph illustrating change in spectrum when a bias voltage isvaried.

FIG. 6 is a graph illustrating change in spectrum when a bias voltage isvaried.

FIG. 7 is a graph illustrating a method of extracting a signal componentof secondary electrons.

FIG. 8 is a flowchart illustrating an example of processing performed byan analysis unit.

FIG. 9 is a flowchart illustrating an example of processing performed byan analysis unit.

FIG. 10 is a diagram illustrating a configuration of an electronmicroscope according to a second embodiment of the invention.

FIG. 11 is a graph illustrating an energy distribution of electronsemitted from a specimen surface when an acceleration voltage is varied.

FIG. 12 is a graph illustrating change in spectrum when an accelerationvoltage is varied.

FIG. 13 is graph illustrating change in spectrum when an accelerationvoltage is varied.

FIG. 14 is a graph illustrating change in spectrum when an accelerationvoltage is varied.

FIG. 15 is a graph illustrating a method of extracting a signalcomponent of backscattered electrons.

FIG. 16 is a flowchart illustrating an example of processing performedby an analysis unit.

FIG. 17 is a flowchart illustrating an example of processing performedby an analysis unit.

FIG. 18 is a diagram illustrating a configuration of an electronmicroscope according to a third embodiment of the invention.

DESCRIPTION OF THE INVENTION

(1) According to an embodiment of the invention, there is provided acharged particle beam device including:

a charged particle beam source;

an analyzer that analyzes and detects particles including secondaryelectrons and backscattered charged particles that are emitted from aspecimen by irradiating the specimen with a primary charged particlebeam emitted from the charged particle beam source;

a bias voltage applying unit that applies a bias voltage to thespecimen; and

an analysis unit that extracts a signal component of the secondaryelectrons based on a first spectrum obtained by detecting the particleswith the analyzer in a state where a first bias voltage is applied tothe specimen, and a second spectrum obtained by detecting the particleswith the analyzer in a state where a second bias voltage different fromthe first bias voltage is applied to the specimen.

The charged particle beam device can extract a signal component of thesecondary electrons based on the first and second spectrums. In thisway, the spectrum of the secondary electrons can be obtained.

(2) According to an embodiment of the invention, there is provided acharged particle beam device including:

a charged particle beam source;

an energy applying unit that varies kinetic energy of a primary chargedparticle beam emitted from the charged particle beam source;

an analyzer that analyzes and detects particles including secondaryelectrons and backscattered charged particles that are emitted from aspecimen by irradiating the specimen with the primary charged particlebeam; and

an analysis unit that extracts a signal component of the backscatteredcharged particles based on a first spectrum obtained by detecting theparticles with the analyzer in a state where the kinetic energy of theprimary charged particle beam has been varied into first kinetic energy,and a second spectrum obtained by detecting the particles with theanalyzer in a state where the kinetic energy of the primary chargedparticle beam has been varied into second kinetic energy different fromthe first kinetic energy.

The charged particle beam device can extract a signal component of thebackscattered charged particles based on the first and second spectrums.In this way, the spectrum of the backscattered charged particles can beobtained.

(3) According to an embodiment of the invention, there is provided ananalysis method for use in a charged particle beam device including acharged particle beam source and an analyzer that analyzes and detectsparticles including secondary electrons and backscattered chargedparticles that are emitted from a specimen by irradiating the specimenwith a primary charged particle beam emitted from the charged particlebeam source, the analysis method including:

obtaining a first spectrum obtained by detecting the particles with theanalyzer in a state where a first bias voltage is applied to thespecimen;

obtaining a second spectrum obtained by detecting the particles with theanalyzer in a state where a second bias voltage different from the firstbias voltage is applied to the specimen; and

extracting a signal component of the secondary electrons based on thefirst spectrum and the second spectrum.

According to the analysis method, a signal component of the secondaryelectrons can be extracted based on the first and second spectrums. Inthis way, the spectrum of the secondary electrons can be obtained.

(4) According to an embodiment of the invention, there is provided ananalysis method for use in a charged particle beam device including acharged particle beam source and an analyzer that analyzes and detectsparticles including secondary electrons and backscattered chargedparticles that are emitted from a specimen by irradiating the specimenwith a primary charged particle beam emitted from the charged particlebeam source, the analysis method including:

obtaining a first spectrum obtained by detecting the particles with theanalyzer in a state where kinetic energy of the primary charged particlebeam has been varied into first kinetic energy;

obtaining a second spectrum obtained by detecting the particles with theanalyzer in a state where the kinetic energy of the primary chargedparticle beam has been varied into second kinetic energy different fromthe first kinetic energy; and

extracting a signal component of the backscattered charged particlesbased on the first spectrum and second spectrum.

According to the analysis method, a signal component of thebackscattered charged particles can be extracted based on the first andsecond spectrums. In this way, the spectrum of the backscattered chargedparticles can be obtained.

Preferred embodiments of the invention are described in detail belowwith reference to the drawings. It is noted that the followingembodiments do not unduly limit the scope of the invention as stated inthe claims. In addition, all of the elements described below are notnecessarily essential requirements of the invention.

In the following, an electron microscope which observes a specimen byemitting an electron beam on the specimen will be described as anexample of a charged particle beam device according to the invention,while the charged particle beam device according to the invention mayinclude a device which observes a specimen by emitting a chargedparticle beam (such as an ion beam) other than an electron beam on thespecimen.

1. First Embodiment 1. 1. Electron Microscope

An electron microscope according to a first embodiment of the inventionwill be described with reference to the drawings. FIG. 1 is a diagramillustrating a configuration of an electron microscope 100 according tothe first embodiment.

As illustrated in FIG. 1, the electron microscope 100 includes anelectron gun 10 (as an example of a charged particle beam source), anacceleration voltage power supply 20, an electron analyzer 30, a biasvoltage applying device 40 (as an example of a bias voltage applyingunit), and an analysis unit 50. Note that the electron microscope 100may be a scanning electron microscope or a transmission electronmicroscope. The electron microscope 100 may be an Auger microprobe.

The electron gun 10 generates an electron beam (an example of a primarycharged particle beam). In the electron gun 10, electrons emitted fromthe cathode are accelerated by acceleration voltage applied between thecathode and the anode and emitted from the electron gun 10. Theacceleration voltage power supply 20 supplies acceleration voltage.

Although not shown, the electron microscope 100 includes an illuminationoptical system for irradiating a specimen with an electron beam. Theillumination optical system directs an electron beam emitted from theelectron gun 10 on the specimen S. The illumination optical system mayinclude a condenser lens, an objective lens, a diaphragm, and adeflector. For example, if the electron microscope 100 is a scanningelectron microscope or a scanning transmission electron microscope, theillumination optical system includes a scanning deflector for scanningthe specimen S with an electron beam.

The electron analyzer 30 detects electrons (an example of particles)including secondary electrons and backscattered electrons (an example ofbackscattered charged particles) emitted from the specimen S onirradiation of the specimen with an electron beam (an example of aprimary charged particle beam). The electron analyzer 30 can divide theincident electrons based on kinetic energy and count the number ofelectrons having particular energy. Using the electron analyzer 30, aspectrum with energy on the abscissa and the number of electrons(intensity) on the ordinate can be obtained. The electron analyzer 30may be an electrostatic hemispherical analyzer.

The bias voltage applying device 40 applies bias voltage to the specimenS. The bias voltage applying device 40 can apply desired bias voltage tothe specimen S. The bias voltage applying device 40 can vary the biasvoltage applied to the specimen S.

The analysis unit 50 obtains an output signal from the electron analyzer30 and obtains a spectrum based on the output signal. The analysis unit50 can extract the signal component of the secondary electrons based ona plurality of spectrums measured under application of different biasvoltages. The analysis unit 50 may include a central processing unit(CPU) and a storage device (such as a random access memory (RAM) and aread only memory (ROM)). The analysis unit 50 performs various kinds ofcomputation processing and various kinds of control processing as theCPU executes a program stored in the storage device.

1.2. Principles

In the electron microscope 100, a specimen S is irradiated with anelectron beam, the electron analyzer 30 detects electrons emitted fromthe specimen S as a result of the irradiation and extracts a signalcomponent of secondary electrons from the spectrum of the electronsobtained by the detection, and the spectrum of the secondary electronscan be obtained. This principle will be described in the following.

FIG. 2 illustrates an energy distribution of electrons emitted from thespecimen surface when the specimen S is irradiated with an electron beamor the energy spectrum of the electrons. FIG. 3 illustrates an energydistribution of electrons emitted from the specimen surface when thebias voltage applied to the specimen is varied.

As illustrated in FIG. 2, the spectrum of electrons emitted from thespecimen surface obtained by irradiating the specimen S with an electronbeam includes a signal component of the secondary electrons and a signalcomponent of the backscattered electrons. The secondary electrons areelectrons excited from the atoms that make up the specimen by inelasticscattering of the electron beam in the specimen. The backscatteredelectrons are backscattered in the process of scattering when thespecimen is irradiated with an electron beam.

When electrons emitted from the specimen surface as a result of electronbeam irradiation are detected by the electron analyzer 30, so that thespectrum thereof is measured, and the bias voltage applied to thespecimen is varied, the signal component of the secondary electronsfluctuates as illustrated in FIG. 3. At the time, the signal componentof the backscattered electrons does not fluctuate. The electrostaticpotential U_(SE) of the secondary electrons at the time is as follows.

U _(SE) =K+P=K+V _(S) +ΔV _(S) (eV)

where K is the kinetic energy, P is the potential energy, V_(S) is thebias voltage, and ΔV_(S) is the variation in the bias voltage.

For example, when the bias voltage V_(S) is set as V_(S)˜0, thesecondary electron peak fluctuates around the original energy value.

FIG. 4 illustrates change in spectrum when the bias voltage applied tothe specimen is varied. FIG. 5 is an enlargement of the low energy sidein FIG. 4, and FIG. 6 is an enlargement of the high energy side in FIG.4. FIGS. 4 to 6 illustrate spectrums when ΔV_(S)=+3 V, ΔV_(S)=+2 V,ΔV_(S)=+1 V, ΔV_(S)=0 V, ΔV_(S)=−1 V, ΔV_(S)=−2 V, and ΔV_(S)=−3 V.

As illustrated in FIG. 5, when the bias voltage is varied, the peaksderived from the secondary electrons fluctuate. In contrast, asillustrated in FIG. 6, the peaks derived from the backscatteredelectrons does not fluctuate. In this way, when the bias voltage appliedto the specimen is varied, the signal component of the secondaryelectrons fluctuates and the signal component of the backscatteredelectrons does not fluctuate.

FIG. 7 illustrates a method of extracting a signal component of thesecondary electrons.

As described above, when the bias voltage applied to the specimen isvaried, a signal component of the secondary electrons fluctuates, and asignal component of the backscattered electrons does not fluctuate.Therefore, for example as illustrated in FIG. 7, a signal component ofthe secondary electrons can be extracted based on a first spectrum S1 ofthe electrons under application of a first bias voltage to the specimenand a second spectrum S2 under application of a second bias voltagedifferent from the first bias voltage to the specimen. For example, thedifference between the first spectrum S1 and the second spectrum S2 canbe determined, and a signal component of the secondary electrons can beextracted based on the difference.

Specifically, when the difference S1−S2 between the first spectrum S1and the second spectrum S2 is obtained, a difference spectrum S3 isobtained as illustrated in FIG. 7. The difference spectrum S3 has thedifference between the intensity of the first spectrum S1 and theintensity of the second spectrum S2 on the ordinate and the electronenergy on the abscissa.

As the signal component of the secondary electrons varies when the biasvoltage is varied, the difference spectrum S3 has for example a pair ofpositive and negative peaks corresponding to the peaks derived from thesecondary electrons in the first and second spectrums S1 and S2. Incontrast, since the peaks derived from the backscattered electrons donot vary even when the bias voltage is varied, the difference spectrumS3 does not have peaks corresponding to the peaks derived from thebackscattered electrons in the first and second spectrums S1 and S2.Therefore, the signal component of the secondary electrons can beextracted by determining the difference S1-S2 between the first spectrumS1 and the second spectrum S2.

1.3. Processing

FIG. 8 is a flowchart illustrating an example of processing performed bythe analysis unit 50.

The analysis unit 50 first obtains a first spectrum (S10). The firstspectrum is obtained by irradiating the specimen S with an electron beamunder application of the first bias voltage to the specimen S by thebias voltage applying device 40 and detecting electrons emitted from thespecimen S by the electron analyzer 30.

Then, the analysis unit 50 obtains the second spectrum (S12). The secondspectrum is obtained by irradiating the specimen S with an electron beamunder application of the second bias voltage different from the firstbias voltage to the specimen S by the bias voltage applying device 40and detecting electrons emitted from the specimen S by the electronanalyzer 30.

Then, the analysis unit 50 extracts a signal component of the secondaryelectrons based on the first and second spectrums (S14). For example,the analysis unit 50 determines the difference between the firstspectrum and the second spectrum and extracts a signal component of thesecondary electrons based on the difference.

The above described processing allows the signal component of thesecondary electrons to be extracted.

1.4. Generation of Secondary Electron Image

In the electron microscope 100, a secondary electron image can beobtained by scanning the specimen S with an electron beam by a scanningdeflector and measuring the first and second spectrums at eachirradiation position on the specimen S.

Specifically, the first and second spectrums are measured at eachirradiation position on the specimen S. For example, at the firstirradiation position, the first bias voltage is applied to the specimenS to measure the first spectrum, and then the second bias voltage isapplied to the specimen S to measure the second spectrum. Similarly, atthe next irradiation position, the first spectrum is measured byapplying the first bias voltage to the specimen S, and then the secondspectrum is measured by applying the second bias voltage to the specimenS. This is repeatedly carried out to determine the first and secondspectrums at each irradiation position on the specimen S.

Note that the first spectrum at each irradiation position may bemeasured by scanning the specimen S with an electron beam underapplication of the first bias voltage to the specimen S, and then thesecond spectrum may be measured by scanning the specimen S with anelectron beam under application of the second bias voltage to thespecimen S.

Then, the analysis unit 50 generates a secondary electron image based onthe first and second spectrums at each irradiation position.

FIG. 9 is a flowchart illustrating an example of processing performed bythe analysis unit 50.

The analysis unit 50 obtains the first and second spectrums at eachirradiation position measured as described above (S20).

Then, the analysis unit 50 extracts a signal component of the secondaryelectrons based on the first and second spectrums at each irradiationposition (S22).

Then, the analysis unit 50 determines the intensity of the secondaryelectrons for each of the irradiation positions (S24). Here, the peak ofthe secondary electrons in the energy spectrum of the electrons isinherent in the substance. Therefore, the intensity of the peak inherentin each element is determined as the intensity of the secondaryelectrons, so that an image representing the distribution of theelements can be obtained. The intensity of the secondary electrons is,for example, a peak to peak value (the difference between the peak valueof a positive peak and the peak value of a negative peak) in thedifference spectrum S3. The intensity of the secondary electrons may bethe integrated intensity of the peak in the difference spectrum S3.

Then, the analysis unit 50 generates a secondary electron image based onthe intensity of the secondary electrons for each irradiation position(S26). For example, a secondary electron image representing theintensity distribution of the secondary electrons is generated byexpressing the intensity of the secondary electrons at each irradiationposition as the brightness of a pixel corresponding to the irradiationposition. When the intensity of a peak inherent in each element isdetermined as the intensity of secondary electrons, an imagerepresenting the distribution of the elements can be generated.

By the above-described processing, a secondary electron image can begenerated.

1.5. Effects

The electron microscope 100 includes an analysis unit 50 which extractsa signal component of the secondary electrons based on the firstspectrum obtained by detecting electrons by the electron analyzer 30under application of the first bias voltage to the specimen S and thesecond spectrum obtained by detecting electrons by the electron analyzer30 under application of the second bias voltage different from the firstbias voltage to the specimen S. In the electron microscope 100, theanalysis unit 50 determines the difference between the first spectrumand the second spectrum and extracts a signal component of the secondaryelectrons based on the difference.

Therefore, the electron microscope 100 can extract a signal component ofthe secondary electrons from the spectrum of electrons emitted from thespecimen S, so that the spectrum of the secondary electrons may beobtained.

For example, using a secondary electron detector which detects secondaryelectrons, secondary electrons and backscattered electrons cannot beclearly distinguished and detected. In contrast, as described above, inthe electron microscope 100, the bias voltage applied to the specimen isvaried, so that a signal component of the secondary electrons isextracted and the spectrum of the secondary electrons is obtained, andthe secondary electrons and backscattered electrons can be distinguishedmore clearly from each other as compared to the case of using thesecondary electrode detector.

In the electron microscope 100, the analysis unit 50 performs processingextracting a signal component of the secondary electrons based on thefirst spectrum and the second spectrum for each irradiation position onthe specimen S, and processing for generating a secondary electron imagerepresenting the distribution of the intensities of the secondaryelectrons based on the intensity of the secondary electrons for eachirradiation position. Therefore, the electron microscope 100 can obtaina secondary electron image less affected by the backscattered electron.

2. Second Embodiment 2.1. Electron Microscope

Hereinafter, an electron microscope according to a second embodiment ofthe invention will be described with reference to the drawings. FIG. 10is a diagram illustrating a configuration of an electron microscope 200according to the second embodiment. In the electron microscope 200according to the second embodiment, the components having the samefunctions as the components of the electron microscope 100 according tothe first embodiment are designated by the same reference characters,and the detailed description thereof will not be provided.

In the electron microscope 100, the bias voltage applied to the specimenS is varied, so that a signal component of the secondary electrons isextracted from the energy spectrum of the electrons emitted from thespecimen S and the spectrum of the secondary electrons is obtained.

In contrast, in the electron microscope 200, the kinetic energy of theelectron beam the electron gun 10 is varied, so that a signal componentof the backscattered electrons is extracted from the energy spectrum ofthe electrons emitted from the specimen S and the spectrum of thebackscattered electron is obtained.

In the electron microscope 200, the kinetic energy of the electron beamis varied by varying the acceleration voltage. The acceleration voltagepower supply 20 includes a variable voltage applying unit 22 whichvaries the acceleration voltage. The acceleration voltage power supply20 functions as an energy applying unit which varies the kinetic energyof the electron beam.

2. 2. Principles

In the electron microscope 200, a specimen S is irradiated with anelectron beam, the electron analyzer 30 detects electrons emitted fromthe specimen S as a result of the irradiation and extracts a signalcomponent of backscattered electrons from the spectrum of the electronsobtained by the detection, and the spectrum of the backscatteredelectrons can be obtained. The principle will be described in thefollowing.

FIG. 11 illustrates a distribution of the energy of electrons emittedfrom the specimen surface when the acceleration voltage is varied.

When electrons emitted from the specimen surface as a result of electronbeam irradiation are detected by the electron analyzer 30, a spectrum ismeasured, and the kinetic energy of the electron beam is varied, asignal component of the backscattered electrons fluctuates asillustrated in FIG. 11. At the time, the signal component of thesecondary electron does not fluctuate. The electrostatic potentialU_(EP) of the backscattered electrons the at the time is as follows.

U _(EP) =K+P=0+E _(P) +ΔE _(P) (eV)

where E_(P) is the acceleration voltage, and ΔE_(P) is the variation inthe acceleration voltage. ΔE_(P) is for example generated by thevariable voltage applying unit 22.

FIG. 12 illustrates change in spectrum when the acceleration voltage isvaried. FIG. 13 is an enlargement of the high energy side in FIG. 12,and FIG. 14 is an enlargement of the low energy side in FIG. 12. FIGS.12 to 14 illustrate spectrums A, B, and C. Note that for the spectrum A,the acceleration voltage is 1990 V (E_(P)=2000 V, ΔE_(P)=−10 V), for thespectrum B, the acceleration voltage is 2000 V (E_(P)=2000 V, ΔE_(P)=0V), and for the spectrum C, the acceleration voltage is 2010 V(E_(P)=2000 V, ΔE_(P)=+10 V).

As illustrated in FIG. 13, when the acceleration voltage is varied, thepeak derived from the backscattered electrons fluctuate. In contrast, asillustrated in FIG. 14, the peak derived from the secondary electronsdoes not vary. In this way, when the acceleration voltage is varied, thesignal component of the backscattered electrons fluctuates, and thesignal component of the secondary electrons does not change.

FIG. 15 is a graph illustrating a method of extracting a signalcomponent of backscattered electrons.

As described above, when the acceleration voltage is varied to vary thekinetic energy of the electrons, the signal component of thebackscattered electrons fluctuates and the signal component of thesecondary electron does not fluctuate. In this way, for example, asillustrated in FIG. 15, a signal component of the backscatteredelectrons can be extracted based on the first spectrum S1 while thekinetic energy of the electrons is set to first kinetic energy, and thesecond spectrum S2 while the kinetic energy of the electrons is set tosecond kinetic energy different from the first kinetic energy. Forexample, the difference between the first spectrum S1 and the secondspectrum S2 can be determined, and a signal component of the secondaryelectrons can be extracted based on the difference.

Specifically, when the difference S1−S2 between the first spectrum S1and the second spectrum S2 is obtained, a difference spectrum S3 isobtained as illustrated in FIG. 15. The difference spectrum S3 has thedifference between the intensity of the first spectrum S1 and theintensity of the second spectrum S2 on the ordinate and the energy ofthe electrons on the abscissa.

When the acceleration voltage is varied to vary the kinetic energy ofthe electrons, the signal component of the backscattered electronsfluctuates, and therefore the difference spectrum S3 has for example apair of positive and negative peaks corresponding to the peaks derivedfrom the secondary electrons in the first and second spectrums S1 andS2. In contrast, since the peak derived from the secondary electronsdoes not fluctuate even when the kinetic energy of the electrons isvaried, the difference spectrum S3 does not have peaks corresponding tothe peaks derived from the secondary electrons in the first and secondspectrums S1 and S2. Therefore, the signal component of thebackscattered electron can be extracted by determining the differenceS1−S2 between the first spectrum S1 and the second spectrum S2.

2. 3. Processing

FIG. 16 is a flowchart for illustrating an example of processing by theanalysis unit 50.

The analysis unit 50 first obtains a first spectrum (S30). The firstspectrum is a spectrum obtained by irradiating a specimen S with anelectron beam and detecting the electrons emitted from the specimen S bythe electron analyzer 30 in a state where the kinetic energy of theelectron beam has been varied into first kinetic energy, or in a statewhere the acceleration voltage power supply 20 is supplying a firstacceleration voltage to the electron gun 10.

Then, the analysis unit 50 obtains a second spectrum (S32). The secondspectrum is a spectrum obtained by irradiating the specimen S with anelectron beam and detecting electrons emitted from the specimen S by theelectron analyzer 30 in a state where the kinetic energy of the electronbeam has been varied into second kinetic energy different from the firstkinetic energy, or in a state where the acceleration voltage powersupply 20 is supplying a second acceleration voltage different from thefirst acceleration voltage to the electron gun 10.

Then, the analysis unit 50 extracts a signal component of thebackscattered electrons based on the first and second spectrums (S34).For example, the analysis unit 50 determines the difference between thefirst spectrum and the second spectrum and extracts a signal componentof the backscattered electrons based on the difference.

The above described processing allows a signal component of thebackscattered electrons to be extracted.

2.4. Generation of Backscattered Electron Images

In the electron microscope 200, a backscattered electron image can beobtained by scanning the specimen S with an electron beam using ascanning deflector and measuring the first and second spectrums at eachirradiation position on the specimen S.

Specifically, first and second spectrums are measured at eachirradiation position on the specimen S. For example, the first spectrumat each irradiation position is measured by scanning the specimen S withan electron beam while the acceleration voltage is a first accelerationvoltage and the kinetic energy of the electrons is first kinetic energy.Then, the second spectrum at each irradiation position is measured byscanning the specimen S with an electron beam while the accelerationvoltage is second acceleration voltage and the kinetic energy of theelectron is second kinetic energy. In this way, the first and secondspectrums at each irradiation position can be obtained.

Then, the analysis unit 50 generates a backscattered electron imagebased on the first and second spectrums at each irradiation position.

FIG. 17 is a flowchart for illustrating an example of processingperformed by the analysis unit 50.

The analysis unit 50 obtains the first and second spectrums at eachirradiation position measured as described above (S40).

Then, the analysis unit 50 extracts a signal component of thebackscattered electrons based on the first and second spectrums for eachirradiation position (S42).

Then, the analysis unit 50 determines the intensity of the backscatteredelectrons for each irradiation position (S44). The intensity of thebackscattered electrons corresponds, for example, to the integratedvalue of the absolute value of the difference between the intensity ofthe first spectrum and the intensity of the second spectrum. Here, thebackscattered electron peaks that appear in the electron's energyspectrum are inherent in the substances. Therefore, by determining theintensities of the peaks inherent in the elements as the intensities ofthe backscattered electrons, an image representing the distribution ofthe elements can be obtained. The intensity is a peak to peak value. Theintensity of the secondary electrons may be the integrated intensity ofthe peaks in the difference spectrum S3.

Then, the analysis unit 50 generates a backscattered electron imagebased on the intensity of the backscattered electrons for eachirradiation position (S46). For example, a backscattered electron imagerepresenting the intensity distribution of the backscattered electronsis generated by expressing the intensity of the backscattered electronsat each irradiation position as the brightness of a pixel correspondingto the irradiation position. When the intensity of a peak inherent ineach element is determined as the intensity of the backscatteredelectrons, an image representing the distribution of elements can begenerated.

By the above-described processing, a backscattered electron image can begenerated.

2.5. Effects

The electron microscope 200 includes the analysis unit 50 which extractsa signal component of backscattered electrons based on a first spectrumobtained by detecting electrons by the electron analyzer 30 in a statewhere the kinetic energy of the electron beam has been varied into firstkinetic energy, and a second spectrum obtained by detecting electrons bythe electron analyzer 30 in a state where the kinetic energy of theelectron beam has been varied into second kinetic energy different fromthe first kinetic energy. The analysis unit 50 determines the differencebetween the first spectrum and the second spectrum and extracts a signalcomponent of the backscattered electrons based on the difference.

Therefore, in the electron microscope 200, a signal component of thebackscattered electrons can be extracted from the spectrum of electronsemitted from the specimen S, and the spectrum of backscattered electronscan be obtained.

For example, even using a backscattered electron detector which detectsbackscattered electrons, the backscattered electron detector cannotclearly distinguish between backscattered electrons and secondaryelectrons. In contrast, in the electron microscope 200, as describedabove, since a signal component of backscattered electrons is extractedby varying the kinetic energy of an electron beam and the spectrum ofthe backscattered electrons is obtained, the backscattered electrons andthe secondary electrons can be distinguished clearly as compared to thecase of using the backscattered electron detector.

In the electron microscope 200, the analysis unit 50 performs processingfor extracting a signal component of the backscattered electrons basedon the first spectrum and the second spectrum at each irradiationposition on the specimen S, and processing for generating abackscattered electron image representing the intensity distribution ofthe backscattered electrons based on the intensity of the backscatteredelectrons at each irradiation position. Therefore, in the electronmicroscope 200, a backscattered electron image less affected bysecondary electrons can be obtained.

In the electron microscope 200, the kinetic energy of the electron beamis varied by varying the acceleration voltage for accelerating theelectron beam. Thus, the kinetic energy of the electron beam can beeasily varied.

3. Third Embodiment

Now, an electron microscope according to a third embodiment of theinvention will be described with reference to the drawings. FIG. 18 is adiagram illustrating a configuration of an electron microscope 300according to the third embodiment. Hereinafter, in the electronmicroscope 300 according to the third embodiment, the components havingthe same function as the components of the electron microscope 100according to the first embodiment and the electron microscope 200according to the second embodiment are denoted by the same referencecharacters, and the detailed explanation thereof will not be provided.

In the electron microscope 100 described above, the bias voltage appliedto the specimen S is varied, so that a signal component of the secondaryelectrons is extracted from the energy spectrum of electrons emittedfrom the specimen S and the spectrum of the secondary electrons isobtained. In the electron microscope 200, the kinetic energy of theelectron beam emitted from the electron gun 10 is varied, so that asignal component of backscattered electrons is extracted from the energyspectrum of electrons emitted from the specimen S, and the spectrum ofthe backscattered electrons is obtained.

In the electron microscope 300, the bias voltage applied to the specimenS is varied, so that a signal component of secondary electrons can beextracted from the energy spectrum of electrons emitted from thespecimen S, and the spectrum of the secondary electrons is obtained.Furthermore, in the electron microscope 300, the kinetic energy of theelectron beam emitted from electron gun 10 is varied, so that a signalcomponent of backscattered electrons can be extracted from the energyspectrum of electrons emitted from specimen S, and the spectrum ofbackscattered electrons is obtained.

In the electron microscope 300, the bias voltage applied to the specimenS can be varied by the bias voltage applying device 40. Also, in theelectron microscope 300, the acceleration voltage power supply 20includes a variable voltage applying unit 22 which varies theacceleration voltage to vary the kinetic energy of the electron beam.

The analysis unit 50 performs processing for extracting a signalcomponent of secondary electrons based on a first spectrum of electronsobtained under application of a first bias voltage to the specimen S anda second spectrum of electrons obtained under application of a secondbias voltage to the specimen S. The analysis unit 50 also performsprocessing for extracting a signal component of backscattered electronsbased on a third spectrum of electrons obtained in a state of thekinetic energy of the electron beam has been varied into first kineticenergy and a fourth spectrum of electrons obtained in a state where thekinetic energy of the electron beam has been varied into second kineticenergy.

Therefore, electron microscope 300 can extract a signal component ofsecondary electrons and a signal component of backscattered electronsfrom the energy spectrum of electrons emitted from the specimen S. Inthis way, the electron microscope 300 can obtain the spectrums ofsecondary electrons and backscattered electrons.

4. Other

It should be noted that the invention is not limited to the embodimentsdescribed above, and various modifications can be made within the scopeof the invention.

According to the first embodiment, a signal component of secondaryelectrons is extracted from the energy spectrum of electrons emittedfrom a specimen on irradiation of the specimen with an electron beam.According to the second embodiment, a signal component of backscatteredelectrons is extracted from the energy spectrum of electrons emittedfrom a specimen on irradiation of the specimen with an electron beam.Meanwhile, in a charged particle beam device according to one embodimentof the invention, a signal component of secondary electrons may beextracted from the spectrum of particles emitted from a specimen onirradiation of the specimen with a primary charged particle beam insteadof the electron beam, or a signal component of backscattered chargedparticles may be extracted from the spectrum of particles emitted from aspecimen on irradiation of the specimen with a primary charged particlebeam.

The backscattered charged particles are backscattered in the process ofscattering when the specimen is irradiated with the primary chargedparticle beam.

The above-described embodiments and modifications are examples and theinvention is not limited thereto. For example, the embodiments and themodifications may be combined appropriately.

The invention is not limited to the embodiments described above andvarious modifications can be made. For example, the invention includesconfigurations that are substantially the same as the configurationsdescribed in the embodiments. Substantially same configurations meansconfigurations that are the same in function, method, and results, orconfigurations that are the same in objective and effects, for example.The invention also includes configurations in which non-essentialelements described in the embodiments are replaced by other elements.The invention also includes configurations having the same effects asthose of the configurations described in the embodiments, orconfigurations capable of achieving the same objectives as those of theconfigurations described in the embodiments. The invention furtherincludes configurations obtained by adding known art to theconfigurations described in the embodiments.

Some embodiments of the invention have been described in detail above,but a person skilled in the art will readily appreciate that variousmodifications can be made from the embodiments without materiallydeparting from the novel teachings and effects of the invention.Accordingly, all such modifications are assumed to be included in thescope of the invention.

What is claimed is:
 1. A charged particle beam device comprising: acharged particle beam source; an analyzer that analyzes and detectsparticles including secondary electrons and backscattered chargedparticles that are emitted from a specimen by irradiating the specimenwith a primary charged particle beam emitted from the charged particlebeam source; a bias voltage applying unit that applies a bias voltage tothe specimen; and an analysis unit that extracts a signal component ofthe secondary electrons based on a first spectrum obtained by detectingthe particles with the analyzer in a state where a first bias voltage isapplied to the specimen, and a second spectrum obtained by detecting theparticles with the analyzer in a state where a second bias voltagedifferent from the first bias voltage is applied to the specimen.
 2. Thecharged particle beam device according to claim 1, wherein the analysisunit obtains a difference between the first spectrum and the secondspectrum and extracts a signal component of the secondary electronsbased on the difference.
 3. The charged particle beam device accordingto claim 1, further comprising a deflector that scans the specimen withthe primary charged particle beam, wherein the analysis unit performs:processing for extracting a signal component of the secondary electronsbased on the first and second spectrums, for each irradiation positionon the specimen; and processing for generating an image representing anintensity distribution of the secondary electrons based on intensity ofthe secondary electrons, for each irradiation position.
 4. The chargedparticle beam device according to claim 1, further comprising an energyapplying unit that varies kinetic energy of the primary charged particlebeam emitted from the charged particle beam source, wherein the analysisunit extracts a signal component of the backscattered charged particlesbased on a third spectrum obtained by detecting the particles with theanalyzer in a state where the kinetic energy of the primary chargedparticle beam has been varied into first kinetic energy, and a fourthspectrum obtained by detecting the particles with the analyzer in astate where the kinetic energy of the primary charged particle beam hasbeen varied into second kinetic energy different from the first kineticenergy.
 5. A charged particle beam device comprising: a charged particlebeam source; an energy applying unit that varies kinetic energy of aprimary charged particle beam emitted from the charged particle beamsource; an analyzer that analyzes and detects particles includingsecondary electrons and backscattered charged particles that are emittedfrom a specimen by irradiating the specimen with the primary chargedparticle beam; and an analysis unit that extracts a signal component ofthe backscattered charged particles based on a first spectrum obtainedby detecting the particles with the analyzer in a state where thekinetic energy of the primary charged particle beam has been varied intofirst kinetic energy, and a second spectrum obtained by detecting theparticles with the analyzer in a state where the kinetic energy of theprimary charged particle beam has been varied into second kinetic energydifferent from the first kinetic energy.
 6. The charged particle beamdevice according to claim 5, wherein the analysis unit obtains adifference between the first spectrum and the second spectrum andextracts a signal component of the backscattered charged particles basedon the difference.
 7. The charged particle beam device according toclaim 5, further comprising a deflector that scans the specimen with theprimary charged particle beam, wherein the analysis unit performs:processing for extracting a signal component of the backscatteredcharged particles based on the first spectrum and the second spectrum,for each irradiation position on the specimen; and processing forgenerating an image representing an intensity distribution of thebackscattered charged particles based on intensity of the backscatteredcharged particles, for each irradiation position.
 8. The chargedparticle beam device according to claim 5, wherein the energy applyingunit varies the kinetic energy of the primary charged particles byvarying an acceleration voltage that is used for accelerating the primecharged particle beam.
 9. An analysis method for use in a chargedparticle beam device including a charged particle beam source and ananalyzer that analyzes and detects particles including secondaryelectrons and backscattered charged particles that are emitted from aspecimen by irradiating the specimen with a primary charged particlebeam emitted from the charged particle beam source, the analysis methodcomprising: obtaining a first spectrum obtained by detecting theparticles with the analyzer in a state where a first bias voltage isapplied to the specimen; obtaining a second spectrum obtained bydetecting the particles with the analyzer in a state where a second biasvoltage different from the first bias voltage is applied to thespecimen; and extracting a signal component of the secondary electronsbased on the first spectrum and the second spectrum.
 10. An analysismethod for use in a charged particle beam device including a chargedparticle beam source and an analyzer that analyzes and detects particlesincluding secondary electrons and backscattered charged particles thatare emitted from a specimen by irradiating the specimen with a primarycharged particle beam emitted from the charged particle beam source, theanalysis method comprising: obtaining a first spectrum obtained bydetecting the particles with the analyzer in a state where kineticenergy of the primary charged particle beam has been varied into firstkinetic energy; obtaining a second spectrum obtained by detecting theparticles with the analyzer in a state where the kinetic energy of theprimary charged particle beam has been varied into second kinetic energydifferent from the first kinetic energy; and extracting a signalcomponent of the backscattered charged particles based on the firstspectrum and the second spectrum.